The present disclosure relates to an electro-optical detector element and to a method of directly reading pixels for alignment purposes.
Over the last few years, electro-optical sensors have been developed that incorporate increasingly higher resolution detectors which, in turn, require systems with higher and higher precision in alignment and pixel co-registration. Indeed, sensor optical systems are now requiring alignment of filters and pixel co-registration to resolutions of less than about 2 microns in order to meet performance requirements.
Current alignment techniques have significant error in alignment at multiple assembly stages relative to the tighter tolerances now required. These stages include detector hybridization stages, sensor chip assembly (SCA) stages, bonding filter alignment stages and optical system alignment stages as well as detector-to-detector alignment stages. Inherent and significant tolerance stack-up issues include, for example, problems with placement accuracies of a read-out integrated circuit (ROIC) relative to a detector during SCA bonding. Such accurate placement requires both precise location and measurement knowledge that can be difficult to obtain. If alignment operations are performed at the electro-optical sensor level, the alignment operations become critical path activities and often require multiple iterations to complete. In some cases, the iterations include cooling operations for focal planes to evaluate the alignment accuracies which result in high cost and significant schedule impact on sensor level integration using iterative alignment methods.
At best, even with the delays and costs associated with alignment operations, current alignment techniques have hybridization errors (e.g., about 4-8 microns), SCA alignment errors, or filter alignment errors (about 20 microns) and total alignment errors (about 25 microns).